Hot work forging die block and method of manufacture thereof

ABSTRACT

A low alloy hot work forging die block characterized by (1) a final low non-metallic inclusion content, especially with respect to silicates and aluminates, due to very low final oxygen and aluminum levels, (2) improved machinability and (3) excellent hardenability, and a method of manufacture thereof which emphasizes oxygen control.

United States Patent Finkl 1 1 Dec. 30, 1975 [54] HOT WORK FORGING DIE BLOCK AND 3,282,683 11/1966 Moore 75/130 R METHOD OF MANUFACTURE THEREOF $332,772 7/ 1%? t 3,336,118 8/1967 Newitt Inventor: Charles Fmkl. Evanston, 3,695,865 10 1972 Wolker 75/130 R [73] Assignee: A. Finkl & Sons Company, Chicago,

Primar Examiner-Peter D. Rosenber y g [22] Filed; May 9, 1973 Attorney, Agent, or Firm-James G. Staples [211 Appl. No.: 358,827

' [57] ABSTRACT [52] CL A low alloy hot work forging die block charactcrizeC [51] Int Cl 2 B221? 9/00 C22C 38/40 i 33/60 by (1) a final low non-metallic inclusion content, es- 1 Field r h 75/128 5 130 5 pecially with respect to silicates and aluminatcs, due ea c h d to very low final oxygen and aluminum levels, (2) im proved machinability and (3) excellent hardenability and a method of manufacture thereof which empha [56] References C'ted sizes oxygen control.

UNITED STATES PATENTS 5/1964 Ruff 75/53 12 Claims, N0 Drawings HOT WORK FORGING DIE BLOCK AND METHOD OF MANUFACTURE THEREOF BACKGROUND OF THE INVENTION Die blocks of the type to which this invention is directed are subjected to unusually severe operating conditions during normal use since, among other things, they are subjected to intermittent heating and cooling from temperatures of, for example, about 300F to about 1 100F and more, heavy impact loads and severe abrasion. Under abnormal working conditions, which invariably occur from time to time in any operation, the die blocks may be subjected to prolonged exposure at high temperatures as where a high temperature workpiece becomes stuck in the dies, or where a large forging is not lifted from the lower cavity between blows. Concurrently with the aforesaid operating conditions the die blocks must be relatively easily machinable, mainly after final heat treatment. And finally the die block must be of substantially uniform hardness at all depths to maximise production after one or more resinkings of the cavity.

SUMMARY OF THE INVENTION C .45 .60 Mn .65 1.25 S .020 .045 P .040 max. Si up to .35 Ni .75 1.25 Cr .60 1.75 Mo .30 .45 v .03 .10 Al .015 max. 2. Ppm 60 max. nppm 2.4 max.

More preferably it is an object to provide a die block having the following preferred composition:

P .025 max.

-continued Ni .85 1.15 Cr .75 1.40 Mo .33 .43

Al less than .005 0 ppm 50 max.

H ppm 2.2 max.

Another object is to provide a die block having the following most preferred composition:

C .53 .57 Mn .75 .95 S .035 aim P .020 max. Si .20 .35 Ni .85 1.05 Cr .85 1.15 Mo .36 .43 V .05 aim A1 less than .005 0 ppm 30 max. H ppm 2.0 max.

Yet another object is to provide a method of making die blocks of the above described chemical composition.

Other objects and advantages of the invention will become apparent from a reading of the foregoing exemplary description of the invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS The product of the invention may be defined by the weight percent of chemical composition as follows:

Broad Preferred Most Preferred C .45 .60 .50 .60 .53 .57 Mn .65 1.25 .75 1.10 .75 .95 S .020 .045 .030 .040 .035 aim P .040 max. .025 max. .020 max. Si up to .35 .20 .35 .20 .35 Ni .75 -1.25 .85 1.15 .85 -1.05 Cr .60- 1.75 .75 1.40 .85 1.15 Mo .30 .45 .33 .43 .36 .43 V .02 .10 .04 .06 .05 aim A1 .015 max less than .005 less than .005 0,, ppm max. 50 max. 30 max. H ppm 2 4 max 2.2 max. 2.0 max.

Carbon is necessary to provide the required wear resistance and hardness. 1f the carbon is significantly higher than 0.60 the die blocks will be subject to breakage in the field. If substantially less than 0.45 carbon is used wear resistance will not be suitable for the extremely strenuous field applications to which the die blocks are subjected. Preferably a minimum of 0.50 carbon is used to ensure good wear resistance and hardness, and maximum production. Most preferably carbon in the range of 0.53 to 0.57 with an aim of 0.55 is used.

Manganese is necessary for hardenability and as a deoxidizer in the steelmaking process. It also functions to control sulphides in forging operations. 1f significantly more than 1.25% manganese is present there is a danger that retained austenite will be present. If substantially less than 0.65% manganese is present the hardenability of the die block may be deleteriously affected. In addition manganese contributes to wear resistance, although to a lesser extent than other carbide formers. Preferably manganese is present in the range of 0.75% to 1.10%, and most preferably from 0.75% to 0.95%. Manganese should be present in an amount at least 20 times the sulphur content to ensure sulphur control.

Sulphur is essential for machinability. 1f the sulphur is significantly above 0.045, or 0.050 at most, an undesirably high quantity of sulphides may be present in the final product. Excess sulphides will deleteriously affect transverse properties. If significantly less than about 0.020 sulphur is present machinability will be adversely affected. Machinability, particularly in the final, hardened condition, is a primary requirement ofa die block. Accordingly, a preferred range, of 0.030 to 0.040 sulphur is desired, with an aim of 0.035. Those skilled in the art will recognize the preferred range and aim as at or above the extreme upper limit for this general type of low alloy steel, electric furnace grade.

Phosphorus can exert a beneficial effect on machinability. However, the deleterious effects of phosphorus in this general type of steel, such as an increase in the transition temperature, outweight any beneficial effects and accordingly the phosphorus content should be kept as low as possible. Under no circumstances should more than 0.040% be present, preferably no more than 0.025%, and most preferably no more than 0.020%. It will be noted that the intentional combination of high sulphur and low phosphorus in this type of steel is unusual.

Silicon is specified for its deoxidizing ability in the steelmaking process. If silicon is present in substantially greater quantities than that specified there is a tendency towards embrittlement of the final product. If the die blocks are made by conventional steelmaking processes the silicon may be in the range of 0.20 to 0.35. However if the molten steel from which the die blocks are made is subjected to carbon deoxidation treatment silicon levels at the lower end of the range may be quite acceptable.

Nickel is required to impart toughness to the die block and strengthen the ferrite. 1f substantially more than 1.25% nickel is present there is a danger of retained austenite and decreased machinability. Excess nickel may also promote hairline cracking which requires scarfing and/or conditioning at the press. 1f substantially less than 0.75% nickel is present than that specified the die block will lack toughness, and hardenability will be reduced, thereby adversely affecting die life in large sections by washing. Preferably nickel should be present in the range of about 0.85 1.15%, and most preferably in the range of 0.85 1.05%.

It has been discovered that copper is substantially interchangeable with nickel up to about 0.5% for the die blocks with which this invention is concerned. Accordingly copper may be substituted for nickel up to about 0.5% copper. However, experience has shown that the nickel content should always be higher than the copper to avoid problems in forging the die blocks. Therefore, the nickel and copper content may be expressed as nickel and/or copper of from about 0.75% to about 1.75%, or other specified range, but not to exceed 0.50% copper, with the nickel content always greater than the copper content.

Chromium is necessary for carbide formation, for hardenability, and for wear resistance. If substantially more than the maximum specified amount of chromium is present the hardening temperature will be too high for normal production heat treatment, and heavy sections will be subject to loose or weak centers. 1f substantially less than the minimum specified quantity of chromium is present the die block will be deficient in 4 wear resistance and hardenability. Preferably chromium is present in the amount of 0.75% to 1.40%, and most preferably from 0.85% to 1.15%.

Molybdenum is one of the most important elements. It is a potent carbide former and contributes to hardenability and wear resistance. Preferably the molybdenum is maintained between 0.33 to 0.43 since this range appears to yield optimum results, although a range of 0.30 to 0.45 may be tolerable. For thick sections it may be desirable to work near the upper end of the broad range, and preferably in the range of 0.36 to 0.43. If the final product is to be a die block of substantial cross-sectional thickness it may be advantageous to increase the molybdenum to a minimum of 0.36 to ensure thorough response to the hardening process.

Vanadium is specified for its grain refining properties. If a significantly greater quantity of vanadium is present than that specified the hardenability of the die block may be decreased due to the insolubility of vanadium carbide at normal treat temperatures. 1f significantly less vanadium is present than that specified the necessary grain refinement may not be achieved. Preferably vanadium is present in the range of 0.03 to 0.10, and most preferably in the range of 0.04 to 0.06, with an aim of 0.05.

Since the amount of aluminum present will also have a significant effect on the quantity of aluminates formed it is desirable to control the melting procedures so as to minimize the amount of aluminum present. The steel should contain, therefore, a maximum of 0.015 aluminum, and preferably less than 0.005 aluminum.

As those skilled in the art will appreciate, there are essentially four types of non-metallic inclusions which, in this type of steel, are considered to be impurities, namely silicates, aluminates, complex oxides and sulphides.

The quantity of silicates and aluminates formed will be substantially proportional to the amount of available oxygen in the steel. The complex oxides are thought to be' formed largely during tapping and teeming. The amount of sulphides formed will, of course, be proportional to the sulphur or sulphur containing materials in the steel, including sulphur from such sources as scrap and oil in turnings and other scrap materials in the shop, the degree to which furnace or vacuum ladle refining is carried out, and intentional additions such as ladle additions of pyrites to meet the desired sulphur specification. Teeming techniques to reduce oxygen pick up may be employed such as the use of a vacuum or inert atmosphere during teeming and/or elimination of splash through the use of splash pads, no dribble teeming techniques or bottom pouring.

The silicates and aluminates are formed as the oxygen comes out of solution due to temperature drop. It is believed that if, at the time the silicates and aluminates are formed, a condition of oxygen starvation in the molten steel exists the oxide and sulphide formation can be very significantly decreased. Accordingly it is essential that steps be taken to ensure low oxygen levels in the steel as will be further described in detail hereafter. For purposes of chemical definition of the die blocks of this invention the quantity of oxygen present in the final product must therefore be less than 60 ppm, preferably less than 50 ppm, and most preferably less than 30 ppm. It will be understood that it is difficult and costly to consistently achieve oxygen levels much below 15 ppm at a carbon content of 0.55% on a commercial production basis, although by careful attention to the practice set out herein such extremely low levels After furnace and tapping ladle treatment the tap have been achieved infrequently. ladle should be subjected to refining under vacuum Single point tool life tests were conducted on a samconditions, preferably by subjection to the simultaple, hereafter referred to as steel B, having the followneous effect of vacuum and purging as illustrated and mg composition: 5 described in greater detail in US. Pat. No. 2,236,635 to C Mn P S Si Ni Cr Mo V Al 02 H2 .56 .84 .018 .035 .30 .94 .93 .36 .048 .005 29 ppm 1.5 ppm which reference is here made for a more detailed understanding. Such vacuum degassing treatment is carried out for a period of time which will enable the oxygen level in the steel to be lowered to under 60 ppm, preferably under 50 ppm, and most preferably under about 30 35 ppm. In a heat of approximately 65 tons the vacuum degassing may for example be carried out for about 10 to 30 minutes, the exact time depending upon the usual process variables encountered in commercial melt shop practice including temperature,

The sample was tested in the annealed condition. and had a BHN of 2l2-222. The test was conducted using M-2 HSS tools, 0.0107 ipr feed, 0.0500 in. depth of cut, and no coolant. Total destruction of the tool was used as the criterion for tool life, and the results were compared to results obtained under identical test conditions with a steel, hereafter referred to as Steel A, having the identical composition except a sulphur content of amount of slag present, and starting gas values.

The vacuum degassing treatment causes flotation of undesirable large non-metallic inclusions into whatever High Speed Steel Tool Stee| Lif at 125 SFPM' Seconds BHN slag may be present on the surface. It will be understood that these inclusions are particularly deleterious A 15 217 3 55 212 in the final product since they adversely affect transverse properties and can function as focal points for stress raisers.

After the two steels were quenched and tempered to The Vacuum degassing "eatmem further ensures BHN 444, single point tests were conducted using C7 reduction of hydrogen into the flake'free regioh- P grade carbide inserts with 5 negative rake angle. Flank riehce has shown that for this yp of Steel the bulk of wear after 548 seconds at 200 SFPM was measured, a large number of heats will be flake free at the PP d th f ll i results w b i level. However, since the failure attributable to flaking,

usually termed thermal rupture is a serious defect it Carbide Tools Flank wear is desirable that the possibility of failure due to flaking Steel at 548 Seconds BHN be minimized as much as possible, and accordingly a A .0064 444 40 maximum of 2.4 ppm is specified. Flaking failures have B .0044 444 occurred even in the 2.3 to 2.4 ppm range and accordingly a maximum of 2.2 ppm is preferred. Recently rare cases of flaking have been experienced at the 2.2 ppm From the foregoing it can be seen that the steel of this level and accordingly 2.0 ppm maximum is the most invention possesses substantially improved machinabilpreferred limit.

ity. To ensure that a thoroughly uniform and controllable In the manufacture of the die blocks of this invention teeming temperature of about 2830F in the ladle will by electric furnace practice it is desirable to make be obtained at the conclusion of the vacuum degassing maximum use of melting scrap of similar composition. treatment, the steel may be subject to intermittent or Conventional electric furnace processing steps may continuous alternating current are heating under vacthen be followed, except as noted below. uum, as more fully described in US. Pat. Nos. Phosphorus removal may be accomplished by utiliza- 3,501,289 and 3,501,290, to which reference is here tion of mill scale at low temperatures, that is, in the made for a more detailed understanding. range of about 2750F to 28401 for example. The mill Other processing steps such as inert gas shroud or scale formed during forging has the desirable ability to vacuum teeming, and/or bottom pouring may be emyield substantial quantities of oxygen to the bath while ployed as necessary to ensure a sound ingot having keeping the bath relatively cool. Slag-off of this initial good surface qualities. oxidizing slag is preferably carried out at low tempera- The silicates and aluminates will be substantially tures, that is, under about 2840F, to remove the P 0 randomly dispersed in such fashion as to minimize their from the molten metal into the slag system. deleterious effects on transverse properties. Further, After furnace processing the steel may be further there will be a reduction in the number of especially deoxidized in the tapping ladle by tapping onto V, FeSi, large sized inclusions in the center of the ingot and a and/or CaSi or other metallic deoxiders. decreased concentration of inclusions near the surface If the sulphur content is below specification at this of the ingot. point resulphurization to reach an aim of 0.035, for A series of commercial 65-ton (nominal size) heats example, may be carried out by the addition of stick containing examples of heats of the aforementioned sulphur, pyrities, or other appropriate sulphur addition broad, preferred, and most preferred ranges are commaterials. piled in the following table:

HEAT TABLE Hcat No. C Mn S Si Ni Cr Mo V Al O H2 138.789 .60 .92 .028 .34 1.02 .98 .39 .051 .005 18 1.5 238,495 .59 .86 .041 .33 .94 1.05 .37 .044 24 1.7 238.500 .53 .94 .022 .22 .91 1.01 .36 .048 N.A.2 2.4 138,791 .56 .95 .027 .26 .95 1.06 .37 .052 26 1.9 138,772 .54 .90 .028 .28 .93 .87 .36 .045 27 1.7 138,770 .57 .87 .034 .34 .96 .87 .36 .043 40 1.9 138.782 .58 .95 .032 .29 .93 1.05 .40 .052 23 1.9 238,498 .56 .94 .031 .31 .93 .98 .36 .053 1.4 138.773 .57 .90 .033 .34 .90 .96 .36 .048 N.A. 1.2

In ppm Not available.

Of especial significance is the very low final Al con- 15 -continued tent and the unusually low oxygen content, which Si ranges down to the 15 ppm level with respect to heat Ni .85 1.15 238,498, for example.

From the foregoing description it will be appreciated v that a unique die block having a low non-metallic inclu- A1 1055 than 005 20 Fe Balance. together with residual. non-deletrious sion content, particularly inclusions of silicates and elements aluminates, good machinability and improved harden- O 50 ppm max. ability, has been disclosed. Various modifications will H2 ppm of course at once occur to those skilled in the art. Accordingly. the scope of the invention should be limited 25 4. The steel die block of claim 3 further characternot by the scope of the foregoing exemplary description, but only by the scope of the hereinafter appended claims when interpreted in light of the pertinent prior art.

1 claim:

1. A low alloy, hot work, forging steel die block, said steel block being characterized by a low-metallic inclusion content, including silicates and aluminates, high machinability in all conditions including final hardened condition, and substantially uniform through hardness in heavy sections, said die block consisting of the following composition by weight percent:

P .040 max.

A1 .015 max.

Fe Balance. together with residual, non-deletrious elements 0 60 ppm max.

H 2.4 ppm max.

2. The steel die block of claim 1 further characterized in that firstly, a maximum of 0.5% copper is present.

secondly, the sum of the nickel and copper is 0.75 to 1.25 by weight percent, and

thirdly, the nickel content is always greater than the copper content.

3. A low alloy, hot work, forging steel die block, said steel die block being characterized by a low non-metallic inclusion content, including silicates and aluminates, high machinability in all conditions including final hardened condition. and substantially uniform through hardness in heavy sections, said steel die blo'ck consisting of the following composition by weight percent:

C .50 .60 Mn .75 1.10 S .030 .040 P .025 max.

ized

firstly, in that sulphide inclusions, where present, are

substantially randomly dispersed, and

secondly, in that said steel is substantially free from large, non-metallic inclusions.

5. A low alloy, hot work, forging steel die block, said steel die block being characterized by a low non-metallic inclusion content, including silicates and aluminates, high machinability in all conditions including final hardened condition, and substantially uniform through hardness in heavy sections, said steel die block consisting of the following composition by weight percent:

S .035 aim P .020 max.

V .05 aim Al less than .005

Fe Balance. together with residual, non-deletrious elements 0 30 ppm max.

H 2.2 ppm max.

6. The steel die block of claim 5 further characterized firstly, in that sulphide inclusions, where present, are

substantially randomly dispersed, and

secondly, in that said steel is substantially free from large, non-metallic inclusions.

7. A forged, low alloy, hot work, steel die block, said forged steel die block being characterized by a low non-metallic inclusion content, including silicates and aluminates, high machinability in all conditions including final hardened condition, and substantially uniform through hardness in heavy sections, said die block consisting of the following composition by weight percent:

C from about .45 to a maximum of about .60 Mn from about .65 to a maximum of about 1.25 S from about .020 to a maximum of about .045 P .040 max.

-contmued Si from about .20 to a maximum of about .35 Ni from about .75 to a maximum of about 1.25 Cr from about .60 a maximum of about 1.75 Mo from about .30 to a maximum of about .45 V from about .03 to a maximum of about .10 Al .015 max." Fe Balance, together with residual, non-deleterious elements 60 ppm max. H 2.4 ppm max.

8. The steel die block of claim 7 further characterized in that firstly, a maximum of .S% copper is present,

secondly, the sum of the nickel and copper is .75% to 1.25% by weight percent, and

thirdly, the nickel content is always greater than the copper content.

9. A forged, low alloy, hot work, steel die block, said forged steel die block being characterized by a low non-metallic inclusion content, including silicates and aluminates, high machinability in all conditions including final hardened condition, and substantially uniform through hardness in heavy sections, said steel die block consisting of the following composition by weight percent:

C from about .50 to a maximum of about .60

Mn from about .75 to a maximum of about 1.10

S from about .030 to a maximum of about .040

P .025 max.

Si from about .20 to a maximum of about .35

Ni from about .85 to a maximum of about 1.15

Cr from about .75 to a maximum of about 1.40

M0 from about .33 to a maximum of about .43

V from about .04 to a maximum of about .06

Al less than .005

Fe Balance, together with residual, non-deleterious elements 0, 50 ppm max.

-continued H, 2.4 ppm max.

to a maximum of about to a maximum of about aim max.

to a maximum of about .35

to a maximum of about 1.05

to a maximum of about 1.15

to a maximum of about .43 .05 aim less than .005

Balance, together with residual, non deleterious elements 30 ppm max. 2 2.2 ppm max.

from about from about S from about from about from about from about from about 12. The steel die block of claim 11 further character ized firstly, in that sulphide inclusions, where present, are

substantially randomly dispersed, and secondly, in that said steel is substantially free from large, non-metallic inclusions. 

1. A low alloy, hot work, forging steel die block, said steel block being characterized by a low-metallic inclusion content, including silicates and aluminates, high machinability in all conditions including final hardened condition, and substantially uniform through hardness in heavy sections, said die block consisting of the following composition by weight percent:
 2. The steel die block of claim 1 further characterized in that firstly, a maximum of 0.5% copper is present. secondly, the sum of the nickel and copper is 0.75 to 1.25 by weight percent, and thirdly, the nickel content is always greater than the copper content.
 3. A low alloy, hot work, forging steel die block, said steel die block being characterized by a low non-metallic inclusion content, including silicates and aluminates, high machinability in all conditions including final hardened condition, and substantially uniform through hardness in heavy sections, said steel die block consisting of the following composition by weight percent:
 4. The steel die block of claim 3 further characterized firstly, in that sulphide inclusions, where present, are substantially randomly dispersed, and secondly, in that said steel is substantially free from large, non-metallic inclusions.
 5. A low alloy, hot work, forging steel die block, said steel die block being characterized by a low noN-metallic inclusion content, including silicates and aluminates, high machinability in all conditions including final hardened condition, and substantially uniform through hardness in heavy sections, said steel die block consisting of the following composition by weight percent:
 6. The steel die block of claim 5 further characterized firstly, in that sulphide inclusions, where present, are substantially randomly dispersed, and secondly, in that said steel is substantially free from large, non-metallic inclusions.
 7. A forged, low alloy, hot work, steel die block, said forged steel die block being characterized by a low non-metallic inclusion content, including silicates and aluminates, high machinability in all conditions including final hardened condition, and substantially uniform through hardness in heavy sections, said die block consisting of the following composition by weight percent:
 8. The steel die block of claim 7 further characterized in that firstly, a maximum of .5% copper is present, secondly, the sum of the nickel and copper is .75% to 1.25% by weight percent, and thirdly, the nickel content is always greater than the copper content.
 9. A forged, low alloy, hot work, steel die block, said forged steel die block being characterized by a low non-metallic inclusion content, including silicates and aluminates, high machinability in all conditions including final hardened condition, and substantially uniform through hardness in heavy sections, said steel die block consisting of the following composition by weight percent:
 10. The steel die block of claim 9 further characterized firstly, in that sulphide inclusions, where present, are substantially randomly dispersed, and secondly, in that said steel is substantially free from large, non-metallic inclusions.
 11. A FORGED, LOW ALLOY, HOT WORK, STEEL DIE BLOCK, SAID FORGED STEEL DIE BLOCK BEING CHARACTERIZED BY A LOW NON-METALLIC INCLUSION CONTENT, INCLUDING SILICATES AND ALUMINATES, HIGH MACHINABILITY IN ALL CONDITIONS INCLUDING FINAL HARDENED CONDITION, AND SUBSTANTIALLY UNIFORM THROUGH HARDNESS IN HEAVY SECTIONS, SAID STEEL DIE BLOCK CONSISTING OF THE FOLLOWING COMPOSITION BY WEIGHT PERCENT:
 12. The steel die block of claim 11 further characterized firstly, in that sulphide inclusions, where present, are substantially randomly dispersed, and secondly, in that said steel is substantially free from large, non-metallic inclusions. 